Gas turbine engine fuel control with plural sleeve valves



GAS TURBINE ENGINE FUEL CONTROL WITH PLURAL SLEEVE VALVES Filed July 22, 1958 June 4, 1963 G. c. MAY ETAL 5 Sheets-Sheet 1 QM, @n www h June 4, 1963 G. c. MAY ETAL GAS TURBINE ENGINE FUEL CONTROL WITH PLURAL SLEEVE VALVES Filed July 22, 1958 5 Sheets-Sheet 2 June 4, 1963 G. c. MAY ETAL 3,091,925

GAS TURBINE ENGINE FUEL CONTROL WITH PLURAL SLEEVE vALvEs Filed July 22, 1958 s sheets-sheet s 3,091,925 GAS TURBINE ENGlNE FUEL CONTROL WITH PLURAL SLEEVE VALVES Gordon Cyril May, Derby, and Charles Gordon Morley,

Ashbourne, England, assignors to Rolls-Royce Limited, Derby, England, a company of Great Britain Filed luly 22, 1953, Ser. No. 750,158 Claims priority, application Great Britain June 11, 1958 12 Claims. (Cl. dll-39.23)

This invention relates to a gas turbine engine fuel system in which fuel liow is metered through :an orice in accordance with ya controlled pressure drop across the orifice.

An object of the invention is to p-rovide a simple hydraulic arrangement which will give reasonably accurate control of acceleration land deceleration and will operate satisfactorily throughout a range of atmospheric pressures.

According to the present invention there is provided a gas turbine engine fuel system .for controlling the supply of pressurized fuel from a source thereof to a burner of |a `gas turbine engine comprising a fuel supply control unit, means in `said control unit providing an orifice, means for supplying pressurized fuel from said source to said burner via said control unit and orice, means for varying the size of the orifice in accordance with engine rotat-ional speed and, independently, in functional relationship with the ratio of the outlet -and intake pressures, P2 `and P1, of a compressor of the engine, and meansv for metering the fuel iiow to the burner in accordance with the pressure drop across the orifice.

Preferably the full liow of fuel from the source to the burner passes through the orifice. This arrangement obviates the use of servo valves which tend to stick and require Lltering of the fuel.

The orifice may be in the form of a slot, the width of which is controlled by means responsive to engine rotational speed, in combination with a movable plate, or a movable aperture, which is adapted to provide an increase or decrease in the area of the orifice directly proportional to the movement imparted to the plate or aperture by means movable in response to the compressor natio i.e. the natio of the outlet to the intake pressure of the compressor.

Preferably, however, the orifice is constituted by aper- Jcures in a pair of relatively movable concentric cylindrical members one of which is mounted closely the other, the means for varying the size of the orifice effecting relative movement of the cylindrical members so as to vary the relative positions of the .apertures therein.

'In order to diminish the risk of sticking between the said concentric cylindrical members it is desirable to arrange that these members are relatively rotatable and relatively slidable axially, the means for varying the size of the orifice effecting relative axial movement of these members, and means being provided for effecting relative rotation lof these members.

Preferably one of said cylindrical members is in two axially spaced parts which are relatively movable axially so as to vary the size of the apen-ture between said parts, at least Vone of said axially spaced parts being relatively rotatable with respect to fthe other cylindrical member. rllhe :other of said cylindrical members may be axially movable and provided with at least one circumferential aperture of varying cross-section axially e.g. of triangular cross-section.

The relative movement of the cylindrical members may be controlled by pressure responsive means, opposite faces of said pressure responsive means being adapted to be supplied with air at the ys-aid pressures P1, P2, or at pressures functionally related thereto. Thus there may be 3,091,925 Patented June 4, 1963 two pressure responsive means connecte-d to diametrically opposite sides of one of said cylindrical members so as to effect axial sliding movement thereof. It will be appreciated that the provision of the two pressure responsive means ensures a balanced push or pull.

Preferably the means for metering the fuel liow Ito the burner in accordance with the pressure drop across the orifice comprises a valve member axially movable in a valve body, the valve member controlling fuel flow from the orifice to the burner, opposite sides of the valve member being subjected to the pressures on opposite side-s respectively of the orifice, the valve member :also being axially positionable in dependence upon engine rotational speed. Desirably, means are provided for effecting relative rotation between the valve member land the valve body.

ln one panticular form of the invention, which is especially suitable for aircraft engines, the orifice is disposed axially Nvithin ia `generally cylindrical control nnit. Preferably the concentric `cylindrical members and the valve member are |also mounted axially within the cylindrical control nnit.

The pressurized fuel can be supplied by any fuel pump such as a centrifugal pump, a variable capacity pump, or a fixed capacity pnmp with an excess flow by-pass or relief valve. If a variable capacity pump is used, `and it is not desired to `'by-pass excess fuel, the pump capacity can be varied in accordance with the pressure of fuel flowing to the burner by applying the latter pressure to a resili'ently-loaded pressure-sensitive device adapted to act-nate a pump capacity changing mechanism.

If desired, the flow to a pilot bur-ner can be taken directly from the downstream side of the orifice so that only the main fuel supply passes through the valve body mentioned above. The liow to the pilot burner can be maintained at all times, rthus avoiding the pse of a pressnrizing valve.

The invention is illustrated, merely by way of example, in the accompanying drawings in which:

FIGURE 1 is a diagrammatic representation of a preferred embodiment of the fuel system according to the invention as applied to a two-shaft ygas turbine engine,

FIGURE 2 is a diagrammatic View of a gas turbine engine having a single stage compressor which is connected to the fuel system shown in FIGURE 1, and

FIGURES 3 `and 3a are graphical representations of the working of the fuel system according to the invention.

Referring now to the drawings, la fuel tank 310l is connected to a fuel control unit 311 by means of a conduit 312 and interposed in the conduit is a main fuel pump 313 which is of the positive displacement type. The control unit 31-1 is generally cylindrical in cross-section and is provided with two chambers 314, 315 which are separated by means of a wall 316, communication between the two chambers 314 and 315 being provided for by means of a bore 317 extending axially through the -wall 316. A spindle 318 passes through and is rotatably mounted in the end wall 319 of the chamber 315. Securely mounted on the spindle 318 at its ends outside and inside the chamber 315 are gear lwheels 32d, 321 respectively. The gear wheel 320 is driven (by means not shown) from the engine.

A sleeve 322 is freely rotatable on a bushed spigot 323 formed on the inner face of the end wall 319. The sleeve 322 is formed integrally at opposite ends with a gear wheel 324 and a radial arm 325, the `gear wheel 324 meshing with the gear wheel 321 on the spindle 318. The radial arm 325 supports t-wo freely rotatable compounded gears 326. The two compounded gears 326 comprise a long face width gear wheel 327 and a gear rwheel 328-. The gear 'wheel 328 meshes with la fixed gear 'wheel 329, carried by the spigot 323, and with teeth 330y formed internally on one end of a first, rotatable, governor housing 3 331. It will be seen therefore that as the gear fwheel 324 is caused to rotate, the gear wheel 328 rotates about the gear wheel 329 with a planetary motion and *because of its interengagement with the internally toothed portion 330 of the housing 331, the housing 331 is also rotated about its axis.

The housing 331 is provided rwith an externally toothed portion 332 on its other end which meshes with a gear Wheel 333. The gear Wheel 333 is carriedfon one end of a freely rotatable shaft 334 'which passes through and is supported in the 'wall 316. Mounted on the other end of the shaft 334 is a further gear -wheel 335 which meshes with an externally toothed portion 336 of a second, rotatable, governor housing 337. Thus the engine drive to the gear Kwheel 320 efects rotation of the housings 331, 337.

The dividing wall 316 is provided with two axially spaced apart aligned bearings 33S, 339 which support between them an axially movable sleeve 340 which is mountedfwithin the said bearings. A rod 341 extends axially through the sleeve 340 and that end thereof which is adjacent the end Wall 319 of the control unit 311 has a gear Wheel 342 mounted thereon, the said gear Wheel 342 meshing 'with the long face Width gear 327 of the two compounded gears 326. The gear 327 will Ithus effect rotation of the sleeve 34d whilst permitting axial movement thereof. The end of the rod 341 remote from the said Wall 319 has a pin 343 mounted therein which is arranged transversely of the rod axis and Ysupports a roller bearing 344 on each of its ends, the bearings 344 being disposed in diametrically opposite axially-extending grooves 345 formed in the bore of a further sleeve 346.

The sleeve 346, which is provided with four, circumferential, triangular apertures 347 which are regularly spaced apart angularly, is supported at one end by the bearing 338 and at its other end .by a bearing 343 formed in a cap member 349 supported Iby the casing of an enlarged end portion 311 of lthe control unit v311. The sleeve 346 is also supported substantially midway of its length by a bearing 350 formed internally of the casing of the control unit 311. One end of the sleeve 346 extends into the sleeve 340 so that the interiors of the two sleeves intercommunicate. l

A llixearing`351 is secured to and mounted on the sleeve 346 and the outer race of the bearing 351 is connected to two diametrically opposed capsules 352 by t-wo diametrically opposed arms 353. Thus, as the capsules 352 collapse and expand, the sleeve 346 moves axially. Each capsule 352 is divided into two compartments 354 and 355 by a dividing Wall 356, the compartment 355 being evacuated. The capsules 352 are housed in the end portion 31.1' of the control unit 311, the said end portion being sealed from communication lwith those parts of the control unit containing fuel.

A sleeve 357 is mounted on the sleeve 346 for axial sliding movements ibut is held against rotation (by means not shown). The sleeve 357 and the bearing 350 are so formed and positioned as to deiine between them a variable area, annular, sharp-edged slot 358.

The sleeve 357 is movable axially #between adjustable stops, not shown, which define the maximum and minimum widths of the slot 35S, variation of the width of the slot 358 is effected by means of a forked member 359 which engages a spring 36) carried by the sleeve, and 1which is intenposed between the member 359 and a flange 377 on the sleeve, the member 359 being connected to the pilots throttle lever 361 in the usual manner.

The Width of the slot 35S is also variable in accordance with engine rotational speed in a manner which will hereinafter be described. Four circumferential apertures 362, which are regularly spaced apart angularly, are provided in the sleeve 340' for communication with two axially spaced por-ts 363 and 364 in the dividing Wall 3i6, the ports 363 and 364 communicating with the primary or pilot and main burners respectively of the gas turbine engine 365.

The engine 365, shown in FIGURE l of the drawings, is provided with a two stage compressor 366 and air (at a pressure P1 which is a function of the compressor intake pressure P1) from a point intermediate of the two stages 367, 368 of the compressor is 4fed into the part 354 of each capsule 352 via a conduit 369, whilst delivery air (at the compressor outlet pressure P2) from the second stage 368 of the compressor 364 is delivered, by way of a conduit 376 from a point intermediate of two restrictors 37% and 37312, in the conduit, into the casing of the part 3l1 so as to surround the capsules 352. It will he seen, therefore, that as the engine speed and compressor delivery pressure P2 increase, the capsules 352 will be progessively collapsed and the sleeve 346 will bel caused to move to the left (as seen in FIGURE 1) and present an increased area of its triangular oriices 347 to the annular orifice 358.

The pressure within the casing 311' externally of the as will be clear from the following explanation.

Flow, at a temperature TlK., through a restriction on opposite sides of which the pressures P2, P1 prevail, may however be shown to be given by:

Mv fr1 Q AF2 f Where A=the area of the restriction and M=the mass flow (see Jamison and Mordell, Ministry of Aircraft Production, R & M No. 2031, 1950).

When, however, the velocity through the restriction becomes sonic, the downstream pressure can no longer influence the flow and Q becomes constant and the oriice is said to be choked Suppose now that the areas of the restrictions 370b. 37611 are A1, A2 respectively and suppose that there is no loss or gain of heat from the system so that gas temperature is the same at each of the restrictions 37017, 37011 and that the mass dow is the same through each of them.

Then

where X=pressure intermediate of the restrictors 370:1, 37% and Within the casing 311.

Eg@ x a,

wea

Where F is a function Whose value depends upon the value of the restrictors 370e, 37017.

Thus the sleeve 346 will be moved in dependence upon the value of In order to pressure balance the sleeve 346 the bore of the bearing 343 is placed in communication with the port 363 by means of a conduit 3-71. Y

Mounted within the first governor housing 331 is a centrifugal governor having weights 372 and arms 373, the arms 373 engaging aiianged sleeve 374 carried on the rod 341. The rod 341 serves to secure the sleeves 340, 374 together so that the position of the sleeve 340' will be controlled by the said centrifugal governor. The gov- 'ernor weights 372 may be of a material of a density about twice the density of the fuel in order to compensate the fuel ow for variations in fuel density.

Similarly, there is mounted within the second governor housing 337 a centrifugal governor having weights 375 (which should be as dense as possible) and arms 376, the arms 376 engaging the ange 377 on the sleeve 357.

In operation, `and assuming that the parts of the apparatus are initially in the position shown in FIGURE l, the chambers 314 and 315 will till with fuel at the outlet pressure of the pump 313 and the said fuel will enter the sleeves 346, 340 via the orilice constituted by the annular slot 358 yand triangular apertures 347. The sleeves 340' will be urged to move to the left (as seen in FIGURE 1) because yof the pressure difference across its internal and external faces, which difference is equal to the pressure drop across the orifice constituted by the annular slot 358 and the apertures 347.

Simultaneously Vwith the urging of the sleeve 340y to the left, the arms 373 of the governor in the housing 331 are moved into engagement with the flanged sleeve 374 by the centrifugal action of the governor weights 372 whereby the said `arms 373 urge the sleeve 340 to the right of the drawing. 'Ihe sleeve 340 will be so positioned by these opposed forces that it meters fuel through the port 363 to the primary burner of the engine and, according to its position, selectively through the port 364 to the main burners of the engine. It will be seen therefore that the position of the apertures 36-2 in relation to the ports 363 and 364 controls the fuel flow through the orifice 347 and 358, since, should the pressure drop across the said orifice become excessive, the sleeve 340 is moved to the left by the pressure difference across its internal and external faces, thereby reducing the vfuel flow to the burners until the pressure drop across the orifice has been reduced, whereupon the governor arms 373 are permitted to move the sleeve to the right to increase the fuel flow to the main burners.

As engine speed increases, the governor arms 373 in the first governor housing 331 move the sleeve 340 further to the right, whereby fuel ilow to the burners is increased. The disposition of the sleeve 340, and hence the flow Vthrough the apertures 362 to the burners, will also be controlled by the pressure difference across the end Wall 340' of the sleeve 340, the opposite faces of this end wall being respectively subjected to the outlet pres-sure of the pump 313 Vand the pressure prevailing downstream of the orifice-347, 358. Simultaneously, as the delivery pressure P2 of the compressor increases, the capsules 352 are progressively collapsed and the sleeve 346 is moved to the left, whereby the triangular apertures 347 present a gradually increasing area to the annular slot 358, and the fuel ow through the ports 363 and 364 is therefore increased.

'Ilhe koperation as so far described is carried out independently of the setting of the throttle `lever 361. When however, the engine rotational speed nears its maximum, for the setting of the throttle lever 361, the governor arms 376 in the second governor housing 337 cause the sleeve 357 to move to .the left, as seen in yFIGURE 1, whereby the width of the slot 358 is reduced and the fuel flow through the sleeve 340 is correspondingly reduced, thereby preventing the rotational speed of the engine exceeding the maximum for the throttle lever setting.

The sleeve 346 will be rotated by the rod 341 relatively to the sleeve 357. Thus if any dirt or ice is entrapped between the sleeves 346, `357 the rotation of the sleeve 346 will reduce the risk .that sticking will prevent axial movement of the sleeve 346. Similarly, the rod 341 will effect relative rotary movement between the sleeve 340' and the bearings 338, 339 and this will reduce the risk that sticking will prevent axial movement of the sleeve 340.

.FIGURE 2 of the drawings shows a gas turbine engine employing a single stage compressor 378 and in this par- 6 ticular case the delivery pressure P2 of the compressor 378 is fed into the intake of the compressor after passing through two restrictors 379 and 380, whilst air is fed, from a point intermediate of the two restrictors, into the casing of the part 311 so as to surround the capsules 352. In this Iarrangement the dividing walls -356 within the capsules are not employed, and the capsules are evacuated.

Means, not shown, but of known kind, are provided for controlling the stroke of the pump 3&13 in accordance with fuel flow to the burners.

During acceleration, the two adjacent edges of the sleeves 357 and bear-ing 350 are moved to their maximum spaced apart distance and the rest of the system acts as an acceleration control unit.

In FIGURE 3, in the upper graph, the ordinate represents engine fuel consumption, (FC) and the abscissa represents engine rotational speed (N). 'Ihe iirm line 50 shows the relationship of these two quantities if no control is exercised, i.e. the pump 3113 is kept in full stroke. The dotted line 51 represents the relationship when acceleration is controlled in accordance with the invention. The chain-dotted line 52 represents the engine demand at steady speed and the chain-dotted line 53 represents conditions when deceleration is controlled in accordance With the invention.

When the acceleration is controlled in accordance with the invention a point 54 will be reached at which it is arranged that the governor 376 will be brought into operation and the yfuel iiow will then drop along `line 55 as the width of `the slot 358 moves from its maximum towards `its minimum value.

In FIGURE 3 the lower graph represents similar conditions for the same range of speeds at a lower P1', similar lines on the graph bearing the same reference numerals as in the upper graph, except for the addition of the sutiix a.

It will be seen that the point 54a and other points on the line 55a are vertically below the corresponding points in the upper graph, :i.e. speed of the engine at which the governor 376 will be brought into operation will be the same at the lower P1 and will not increase as is frequently the case with existing systems.

In FIGURE 3a, the ordinate of the graph represents FC P1N while the abscissa represents the engine compressor ratio The line 516 is Ithe compressor surge line; that is to say,l

the shaded area whose limit is defined by the line 56 is the area in which surging of the .compressor occurs. It will be noted that the surge line 56 has a dip v56a in it at moderate pressure ratios.

The heavy line I52b is the steady running line; that is to say the line S'Zb, like the llines 5\2 and 52a, represents the lfuel consumption at steady engine speeds.

rl`=he full line `51b like the lines 5-1, 51a, is the preferred acceleration line; that is to say the line 5.1b represents the preferred relationship when accelerat-ion is controlled in accordance with the invention. It is of course essential to ensure that .the acceleration control line 51h is disposed between and does not cut the lines 56, 52h. If the acceleration .control line 51b cuts the line 56, surging of the compressor will occur, whilst if the acceleration control line 51h cuts the line 52h, insuflicient fuel will be provided at so-me stage to keep the engine running at steady speed.

As stated above, in the fuel system of the present invention the fuel is metered to the engine in response both to engine rotational speed and to The simplest possible form of .the function could be lobtained by evacuating the capsules 3'52 and applying the pressure P2 to the outside of them, the capsules 352 having a displacement proportional to the total force acting on them. This would, however, produce an acceleration control line 511C in the form of a straight line passing through t-he origin, and this straight line were arranged -to miss the dip 56a in the surge line 56v it would cut the steady running line 521; at A. This would mean that a. very powerful starter motor would be needed to speed the engine up past the point A.

Alternatively the arrangement could be such that the capsules 352 did not completely close the metering orifice even at zero pressure. This, however, would result in an excessive fuel supply when the aircraft was flying at a high altitude.

IIt is therefore important that the part of .the acceleration control line Sib `corresponding to low compressor ratios should lbe .curved so as to liebetween the surge line 56 and steady running line 5i2b. This is effected in practice .by reason of the fact that the casing 311', Within which the capsules 352 are mounted, is connected to sources of P1 .and P2 by way of the restrictors 37011, 37019 respectively.

When the air fiow through the restrictor 37th: reaches the velocity of sound it is said to choke and the value of the pressure P1 downstream of it cannot infiuence the mass flow therethrough or the pressure upstream of it. Thus once the restrictor 3700i chokes, the pressure in the casing 311 will be a constant fraction of P2 no matter whether the restrictor 37011V is ,choked or not. Thus once choking occurs, the portion BC of the acceleration control line 51C will be obtained.

At low compressor ratios P 1' however, the restrictor 3700: will be unchoked` and the flow through it Will be less thanunder choking conditions. The pressure drop across the restrictor 37011 will therefore be reduced and the pressure in the casing 31T will be nearer to P2. In the limit at starting conditions, P2=P1=the pressure of the `casing 311', since there will be no pressure drop .and no ow. At starting conditions, the pressure P2 will therefore be applied to the capsules 352. This, therefore, will produce La curved acceleration line DB which merges into the straight line BC.

The position of B on the acceleration line DBC can be 'altered by altering the shape of the restrictor 37 0a.

yIt will be noted that the line BC tends to approach the steady running line 52b at high pressure ratios. This tends to result in -slow accelerations at high pressure ratios fand also leads to a variation in governed speed with varying day temperature for any given setting of the spring 360 of the governor 376. Y

As regards the said variation in governed speed, this occurs because, if the engine inlet temperature T1 varies, a given value of speed will be a variable value of N T (and therefore P2/P1' since there isa functional relationship between N/\/T and P2/P1'). Suppose for example, that at a given setting of the spring 360 of the governor 376 and at a high T1, the governor 376 starts to reduce the size of the slot 358 at a point K1 on the line BC. The :fuel fiow will, say, be reduced along a line K1L1 as the speed increases, the line K1L1 intersecting the steady running line 52b at M1, whereby the controlled engine speed (corresponding to M1) will be -a calculable amount above the speed corresponding to K1.

At a lower value of T1, however, the governor 376 will start to reduce the size of the slot 358 at the same speed N and therefore at a higher value of N/.\/1- and of P2/ P1'. VAccordingly the governor 376 will start to reduce '8 .the size of theslot 358 at, say, a point K2 on the line BC, the fuel flow being reduced along a line K2L2 which intersects the line 52b at M2.

As will be seen Ifrom FIGURE 3a, the reduction of fuel flow between K2 and M2 is a smaller fraction of the initial fuel flow than the reduction of fuel flow between K1 and M1. The slot 358 will not therefore have to close so far -to reduce fuel iiow from K2 to steady running conditions at M2 -as it will have to close to reduce fuel iiow from K1 to steady running conditions at M1. Moreover, although the point M2 represents a higher speed than the point K2, the speed differential between these points is smaller than between the points K1 and M1. In other Words, as T1 falls, there is a corresponding reduction in the increase of engine speed which occurs from the point where the governor 376 starts to reduce the size of the slot 35S to the point where steady running conditions are reached. Accordingly the speed to which the engine is controlled will fall with T1.

A preferred Ifeature of the present invention is there- `fore to provide means which ensure that the controlled speed does not substantially vary with T1. This is effected by causing the fuel supply to be controlled as indicated by the preferred acceleration line 51b, the line 5111` having a straight portion EG which, if produced, would cut the zero fuel axis at approximately the same point H as would be cut by -a straight portion QR of the steady running line 521; if the straight portion QR were produced.

In FIGURE 3a, the acceleration line 51b is shown as passing through the point K1 which corresponds to a high T1. At -a high T1, fuel iiow Will therefore continue to be reduced along the lline K1M1L1. At a low T1, however, fuel flow will now be reduced along a line K2', M2', L2. The engine will therefore reach steady running conditions at M2' which is a slightly higher speed than M2.

It will be appreciated'that the relative disposition of `the parts EG and RQ of the lines Sib, 5219 is such that ythe percentage reduction in 4fuel flow between K2' and M2' will be substantially the same as between K1 and M1. The size of the slot 358 will therefore be reduced to substantially the same extent, and the final controlled speed will be substantially the same, at all inlet temperatures.

An acceleration line 51h of the shape shown in FIG- URE 3a can be obtained by opening at least part of the capsules 352 to the pressure P1 instead of evacuating the whole of the capsules. The proportion of the capsules 352 which is open to the pressure P1' is chosen to give the required point H on the line GE produced.

' As stated above, the pressure in the casing 311' is v respectively subjected to P1 and to a pressure functionally related to P1' namely 1. A (gas turbine engine fuel system for controlling the supply of pressurized fuel from `a source thereof to a burner of Ia gas turbine engine for burning in air from a compressor forming a part of said engine comprising a substantially `cylindrical fuel supply unit, means arranged in land on the axis of .said supply unit providing a metering orifice, means for supplying pressurized fuel from said source 'to said burner via said metering orifice, speed responsive means mechanically connected to the means providing the metering orifice to vary the size of the metering orifice in accordance with engine rotational speed, a conduit opposite ends kof which are adapted to be supplied with air Iat pressures functionally related to the pressures of the inlet and outlet ends of said compressor, a pair of spaced restrictions in said conduit, a pressure responsive means mechanically connected to the means providing the metering orifice to vary the size of the metering orifice, means for applying to the exterior of 4said pressure responsive means the pressure in the space between said rest1ictions, a part of the pressure responsive means being evacuated and another part thereof being opened to air at the said pressure functionally related to the compressor inlet pressure land means rfor throttling the fuel iiow to the burner in response to the pressure drop across the metering orifice.

2. A gas turbine engine fuel system as claimed in claim l in which the pressure responsive means comprises a bellows mounted in a chamber, said chamber communicating with the -space between the restrictions.

3. A gas turbine engine fuel system for controlling the supply of pressurized fuel from a source thereof to a burner of a gas turbine engine comprising means providing a metering orifice, means for supplying pressurized fuel from said source at full pressure to -said metering orifice, means to deliver fuel from the orifice to said burner, speed responsive means mechanically connected to the -means providing the metering orifice, the speed responsive means varying the size of the metering orifice in accordance with engine rotational speed, a chamber, a bellows mounted within the chamber and mechanically connected to the means providing the metering orifice so as to vary the size of the `latter, said bellows having two serially arranged compartments, means for supplying the interior of one of the compartments of the bellows with air at a pressure functionally related to the compressor inlet pressure, the other compartment being partially evacuated, a pair of passages communicating with said chamber and respectively adapted to be supplied with air at pressures functionally related to the pressures of the inlet land outlet ends of a compressor of the engine, a restriction in each said passages, and means for throttling the fuel fiow from the oriee to the burner in accordance with the pressure drop across the metering orifice.

4. A gas turbine engine fuel system for controlling the supply of pressurized fuel from a source thereof to a burner of a lgas turbine engine comprising means providing a metering orifice, means for supplying pressurized fuel from said source to said burner via said metering orifice, speed responsive means mechanically connected to the means providing the metering orifice, the speed responsive means varying the size of the metering orifice in accordance with engine rotational speed, adjustable stops engageable with the means providing the metering orifice, said stops cont-rolling the extent to which the size of the metering orifice may be varied by the speed responsive means, a chamber, a bellows having a part evacuated mounted within the chamber and mechanically connected to the means providing the metering orifice so ras to vary the size of the latter, means for supplying an- Iother tandem arranged part of the interior of the bellows with air at a pressure functionally related to the compressor inlet pressure, a pair yof passages communicating with said chamber and respectively adapted to be supplied with air at pressures functionally related to the pressures of the inlet and outlet ends of a compressor of the engine, a restriction in each :said passages, and means for throttling the fuel flow from `the orifice to the burner in accordance with the pressure drop across the metering orifice.

`5. A gas turbine `engine -fuel system for controlling the supply of pressurized fuel from a source thereof to main and pilot burners of a :gas turbine engine for burning in air from a compressor forming a part of said engine, comprising, a substantially cylindrical fuel supply unit, means arranged in and on the axis of said supply unit providing -a metering orice, a duct for supplying pressurized fuel from said source to said metering orifice, a first means on said axis responsive to engine rotational speed, an axially movable mechanical connection connecting said first means to the means providing a meterting orifice, said first means reducing the size of the metering orifice when a predetermined engine rotational speed is reached, a chamber, pressure responsive means mounted in said chamber, means for subjecting -the exterior of said pressure responsive means to pressures functionally related to the pressures `of the inlet and outlet ends of said compressor, lan axially movable mechanical connection which directly connects the pressure responsive means to the means providing the metering orifice and which extends through the chamber and into said duct, means for effecting relative rotation of said axially movable mechanical connections, first and second conduits for conveying fuel from ra downstream side of said metering orifice respectively to said main and pilot burners, a throttle valve on said axis for controlling fuel liow through said rst conduit, means directly employing the fuel pressure immediately upstream of said metering orifice to urge said throttle valve in a valve closing direction, means directly employing `the fuel pressure immediately downstream of said metering orifice to urge said throttle valve in a valve opening direction, and `a second means on said axis responsive to engine rotational speed connected for urging said throttle valve in the valve opening direction with a pressure which increases with increasing engine rotational speed.

6. A gas turbine engine fuel system for controlling the supply of pressurized fuel from a source thereof to main and pilot burners of a gas turbine engine for burning in `air from a compressor forming part of said engine comprising a substantially cylindrical fuel supply unit, means arranged in and on the axis of said supply unit providing a metering orifice, a duct for supplying pressurized fuel from said source to said metering orifice, a first means responsive to engine rotational speed, an axially movable mechanical connection which rdinectly connects the means providing the metering orifice to the said first means, said first means reducing the size of the metering orifice only when a predetermined engine rotational speed is reached, manual means to regulate said predetermined speed, a chamber, pressure responsive means mounted in said chamber, means -for subjecting the pressure responsive means to pressures functionally related to the pressure of the inlet and outlet ends of said compressor, an axially movable mechanical connection which directly connects the pressure responsive means to the means providing the metering orifice and which extends through the chamber and into said duct, means for effecting rotation of both said axially movable mechanical connections, first and second conduits 4for conveying fuel from the downstream side of `said metering orifice respectively -to said main and pilot lburners, a throttle valve on said axis for controlling fuel fiow through said first conduit, means for employing the fuel pressure immediately upstream of said metering :orifice to urge said throttle valve in a valve closing direction, means for employing the fuel pressure immediately downstream of said metering orifice to urge said throttle valve Ain a valve opening -direction and a second means continuously responsive toengine rotational speed for urging said throttle valve in the valve opening direction with a pressure which increases with increasing engine rotational speed, the construction being such that the lfull flow lof fuel from said source to said burners passes through said duct, said metering orice, said conduits and said throttle valve.

7. A gas turbine engine fuel system for controlling the supply of pressurized fuel from a source thereof to main and pilot burners of a gas turbine engine, comprising a substantially cylindrical fuel supply unit, a pair of 'aperturred sleeve-s axially mounted therein the one Within the other for relative laxial movement, the apertures in said sleeves cooperating with each Iother to provide -a metering orifice, means for effecting relative `rotation of said sleeves, means for supplying pressurized fuel from said Source -to said metering orifice, a first means responsive to engine rotational speed, an axially movable mechanical connection which directly connects the said -rst means to one of said sleeves, said first means effecting relative axial movement of said sleeves so as to reduce the size of the metering orifice only when a predetermined engine rotational speed is reached, a chamber, pressure responsive means mounted in said chamber, means for subjecting the pressure responsive means to pressures functionally related to the pressure of the inlet and outlet ends of said compressor, an axially movable mechanical connection which -directly connects the pressure responsive means Ito one of said sleeves, said pressure responsive means effecting relative axial movement of said sleeves so as to increase the sizeof the metering orifice in functional relationship with increase in the ratio of said pressures, means for effecting rotation of vboth said axially movable mechanical connections, first and second conduits for conveying fuel from the downstream side of said metering orifice, respectively to s-aid main ,and pilot burners, a throttle valve 4on said axis for controlling fuel flow through said rst conduit, means ernploying the zfuel pressure immediately upstream of said metering orifice to urge said throttle valve in la valve closing direction, means employing the fuel pressure immediately `downstream of said metering orifice ,to urge said throttle valve in a valve opening direction, and a second means continuously responsive to engine rotational speed for urging -said throttle valve in the valve opening direction with a pressure which increases with increasing engine rotation-al speed.

8. A gas turbine engine fuel system -for controlling the supplyof pressurized fuel from a source thereof to main land pilot burners of a gas turbine engine, comprising a substantially cylindrical fuel supply unit, a pair of apertured sleeves axially mounted therein the one within the other for relative axial movement, one of said sleeves being in two axially spaced parts which are relatively movable axially so as to vary the size of the aperture between said parts, Vthe apertures in said sleeves cooperating with each other to provide a metering orifice, means for rela-tively rotatingsaid sleeves,- means `for sup'- .plying pressurized -fuel from said source to the outer `side of said metering orifice, a first centrifugal governor, an axially movable mechanical connection which directly connects the first centrifugal governor lto one :of said :axially spaced parts, said centrifugal governor being arranged to reduce the space between the said axially spaced parts when apredetermined engine rotational speed is reached, :a chamber, pressure responsive means mounted in said chamber, means or subjecting the pressure responsive means to pressures functionally related to the pressure of the inlet and outlet ends of -said compressor, an axially movable mechanical connection which directly connects the pressure responsive means to the other vsleeve for effecting relative axial movement to the sleeves so as to increase the size of the metering orifice in functional relationship With increase in the ratio of said pressures, first and second conduits for conveying fuelrfrom the downstream side of said metering orifice through said sleeves and respectively to said main and pilot burners, a throttle valve co-axial with said sleeves for controlling 4fuel flow through said first conduit, means for employing the fuel pressure immediately upstream of said metering'orifice to urge said throttle valve in a valve closing directiom means for employing the fuel pressure immediately downstream of `the said metering orifice to urge said throttle valve in a valve opening direction, a second centrifugal 'governor continuously urging said throttle valve in the valve opening direction with apressure which increases with increasing engine rotational speed, a pair of housings rotatably mounted in the supply -unit for rotation about the Vaxis thereof, and ydrive means drivable from the gas turbine engine for etecting rotation of the housing and sleeves, one of said governors being mounted in and rotated by each housing.

9. A gas turbine engine fuel Isystem as claimed in claim 8 in which lthe pressure responsive means comprises two pressure responsive devices remote from the axis and connected to dia-metrically opposite sides of one of the sleeves so as to effect axial sliding movement thereof.

l0. A gas turbine engine fuel system for controlling the supply of pressurized fuel from a source thereof to the burners of a gas turbine engine comprising means providing a metering orifice, a conduit for supplying pressurized fuel from said source to said metering orifice at full pressure and through it to said burner, a chamber, a bellows having two compartments tandem, mounted in said chamber, one of said compartments being partly evacuated, means for supplying the other compartment of the bellows with air at a pressure functionally related to the pressure of the inlet end of a compressor of the engine, a pair of passages communicating with said chamber and respectively Vadapted to be supplied with air at pressures functionally related to the pressures of the inlet .and outlet ends of the compressor, la restriction in each 'said passage, an axially movable mechanical conneotion which directly connects the bellows to the means providing the metering orice and which extends through the chamber and into the said conduit, and means for effecting rotation of said axially movable mechanical connection.

1l. A gas turbine engine fuel system as defined in claim 10 in which means is provided for effecting pressure balancing of the said axially movable mechanical connection.

12. A gas turbine engine fuel system for controlling the supply of pressurized fuel from a source thereof to the burners of a gas turbine engine comprising means providing a metering orifice, a conduit for supplying pressurized Afuel from said source to said metering orifice at full pressure and through i-t to said burners, a chlamber, a bellows mounted in said chamber `and having two series arranged compartments with one partly evacuated, means for supplying the other compartment of the bellows with air at ra pressure functionally related -to the pressure of the inlet end cfa compressor of the engine, a pair -of passages communicating with said chamber land respectively adapted to be supplied With air lat pressures functionally related to the pressures of the inlet and outlet ends of the compressor, -a restriction in each said passage, a first axially movable mechanical connection which directly connects the bellows to the means providing the metering orifice and which extends through the chamber and into the said conduit, speed responsive means responsive to engine rotational speed, a second :axially movable mechanical connection which directly connects the speed responsive means and the means providing the metering orifice, and means for effecting notation of said lfirst and second axially movable mechanical connections.

References Cited in the file of this patent UNITED STATES PATENTS 2,593,536 Chamberlin et al Apr. 22, 1952 2,668,416 Lee Feb. 9, 1954 2,670,599 Davies et al. Mar. 2, 1954 2,714,803 Abild Aug. 9, 1955 2,836,957 Fox lune 3, 1958 2,856,754 Torell Oct. 21, 1958 2,858,700 Rose Nov. 4, 1958 2,861,420 Lewis Nov. 25, 1958 2,934,898 Graefe May 3, 1960 2,950,596 Haase et yal Aug. 30, 1960 FOREIGN PATENTS 211,974 Australia June 7, 1956 646,780 Great Britain Nov. 29, 1950 716,254 Great Britain Sept. 29, 1954 771,841 Great Britain Apr. 3, 1957l 

